The way he intended to do this was a bit special however as he wanted to shift the true shape of the soul much like one would edit an image or sentence. Nick wanted to remove the parts that felt redundant and shift that mass to what he saw as improvements. The beetles for example lacked magical abilities and were basically at the bottom of the food chain for animals. He wanted to see if it was possible to change that somehow. His first experiment in this regard had him take out the soul of a beetle and then begin to clumsily he will admit manipulate the shape of the soul.-
First he removed the middle set of legs and used that mass to improve the shape and power of the remaining four slightly. Then he began to narrow the beetles body shape with it coming out like a needle point arrowhead. He then put this newly modified soul back into the body he took it from originally and watched as the body began to change shape. The final result was fatter than he made the souls shape but the general form of the beetle remained as he designed.-
Unfortunately the bug died shortly afterwards from the organs not being designed for this new body type. 'Hmm I wonder if that is true for the other creature as well but it isn't showing signs of it because the failures are taking longer to manifest?' Nick pondered while looking at the rat beetle hybrid abomination. The creature didn't seem to be in pain or suffering and was even wondering about in the isolated area it was in in a bored manner. Nick cast a medical spell he learned from Slytherins library that allowed one to gaze into the internal workings of a body without harming the one it was cast on.-
It was merely one of the many high end specialized spells that Nick had learned from absorbing the mans life's worth of knowledge. Slytherin didn't do it by half when writing down his life in the library and it was almost as if he was personally teaching Nick all that he knew. Mana wise Nick was weaker than Snape and most of the professors but in terms of knowledge he likely only fell short of Dumbledore in the school. That was after only completing half of Slytherins library to boot.-
Nick wasn't sure whether or not Dumbledore had more or less knowledge on magic than Slytherin. What he did know was that after he finished absorbing the contents of the library he would definitely have the knowledge of a powerful tier four wizard at the least. Anyways the spell allowed Nick to see that not only was the abominations organs not slowly failing they even seemed to be improved instead! 'What is the difference between the two transformations? Both are clearly unnatural but one caused the death of the test subject while the other only made it stronger.' Nick pondered seriously.-
It was a fascinating difference that fueled his curiosity in the subject of souls even further as it was such a complex and wide topic. Even in the first half of Slytherins library Nick had seen only three mentions on the topic and those were merely uses of it the founder had personally seen. Sadly the medical magics that were in the first half of the library focused exclusively on the mind and body such as curses , poisons and mental wounds. Even in the library of Hogwarts there was a tiny amount of books on souls and all of them minus two were books on dark magic.-
After pondering it for a moment Nick developed a theory on why the two different approaches to the same result had different results in the end. Basically all souls "knew" what they and by extension the body was supposed to be like and acted on the body to manifest this. By forcefully altering the shape and function of the soul Nick had introduced imperfections in this "knowledge" that translated to the body not being able to cope with it as some parts didn't know they needed to change as well.-
In the case were one soul devoured the other however the entirety of the soul was overhauled and improved thus meaning there were no imperfections in the design of the "knowledge". Nick could only frown at this though since if true it meant that to manually alter a soul he needed to either change literally every facet of the souls form himself which was way more effort than it was worth in the case of simple bugs or rats. Or he needed to limit the changes to the soul to less fundamental things like small upgrades to the legs.